1. Field of the Invention
The present invention relates to a mobile vehicular apparatus which has a telescopic boom supporting on its tip end an aerial cabin or platform for carrying an operator, a manipulator device, and a working device such as a crane.
2. Description of the Prior Art
FIG. 7 of the accompanying drawings shows a conventional mobile vehicular apparatus, generally denoted at 50, which is arranged to perform various aerial jobs or tasks. The mobile vehicular apparatus 50 has a telescopic boom 51 with a cabin support shaft 52 vertically mounted on its tip end. The cabin support shaft 52 supports thereon an aerial control cabin 53 which can rotate with respect to the boom 51. The aerial control cabin 53 supports a manipulator device 55 which is forward of the cabin support shaft 52 and an auxiliary boom 54 above cabin support shaft 52. The control cabin 53 is movable in a spatial range that is a combination of the range in which the boom 51 can be raised and lowered, extended and contracted, and turned, and the range in which the control cabin 53 can be rotated about the cabin support shaft 52.
When the boom 51 is fixed in the position shown in FIG. 7 and a transformer 56 is suspended by the auxiliary boom 54, the auxiliary boom 54 is subjected to a considerable bending moment M because of the weight of the control cabin 53 and the weight of the transformer 56. If the control cabin 53 is turned while the transformer 56 is being suspended by the auxiliary boom 54, then the auxiliary 54 is also subjected to a large torsional moment T due to the above weights. As a result, a very high contact pressure is applied to a boom receiver C of the boom 51.
The mobile vehicular apparatus 50 is usually used to process or service "hot" or energized electric cables. Therefore, a distal boom member 51a of the boom 51 is normally made of FRP (Fiber Reinforced Plastic) which is a highly electrically insulating material. Because the FRP material selected for the distal boom member 51a must have excellent mechanical strength to withstand the contact pressure applied thereto, the boom 50 is expensive and requires careful maintenance.
FIG. 8 shows the manner in which aerial electric cables W1 through W3, corresponding to first, second, and third phases, are installed on a post using the mobile vehicular apparatus 50. For such installation, the mobile vehicular apparatus 50 is positioned as closely to the shoulder of the road as possible, the boom 51 is set to the best position, the control cabin 53 is rotated, and the manipulator device 55 or the auxiliary boom 54 is operated. The control cabin 53, the auxiliary boom 54, and the manipulator device 55 of the conventional design are rotatable in only a limited range about the vertical cabin support shaft 52. Therefore, when the control cabin 53 is held in the solid-line position in FIG. 8 and the manipulator device 55 is actuated to install the aerial electric cables W1 through W3, the manipulator device 55 often can install only first- and second-phase cables W1, W2 even if it is moved as far forwardly as possible toward the cables W1 through W3. In order to install the third-phase cable W3 that is located farthest from the manipulator device 50, the position of the mobile vehicular apparatus 50 must be changed and the boom 51 must be raised and lowered, extended and contracted, and turned once more until the control cabin 53 is repositioned at the position indicated by the imaginary lines in FIG. 8.
When the mobile vehicular apparatus 50 is to be thus moved, the outriggers for supporting the mobile vehicle have to be retracted and the control cabin 53 has to be lowered into a safe low position. Even if the control cabin 53 can be moved to the imaginary-line position through the adjustment of the boom 51 while the mobile vehicular apparatus 50 remains unchanged in position, the operator in the control cabin 53 is required to manipulate a plurality of control levers in a complex sequence. Such a control procedure is highly tedious and time-consuming to perform and also inefficient.